This invention relates to an improved surface coating composition capable of forming stable films having excellent protective properties, especially on metallic substrates. In particular the present invention is directed to an improved vinylidene chloride interpolymer latex for use as a metal coating.
The use of vinylidene chloride polymers as coatings is known. For example, U.S. Pat. Nos. 4,341,679 and 4,435,478 disclose coatings for metallic substrates where the polymer consists essentially of vinylidene chloride, vinyl chloride, an alkyl acrylate or methacrylate, and an unsaturated carboxylic acid. U.S. Pat. Nos. 4,945,134 and 5,039,751 disclose vinylidene chloride copolymers having barrier properties for use as a coating on polymer films which comprise vinylidene chloride monomers as a first phase interpolymerized with ethylenically unsaturated monomers, such as alkyl acrylates or methacrylates, or acrylic or methacrylic acid as a second phase. U.S. Pat. No. 3,291,769 teaches a process for manufacturing polyvinylidene chloride emulsions used as barrier coatings on paper and films. U.S. Pat. No. 3,787,232 discloses vinylidene chloride polymers capable of being cured at low temperatures for use as coatings for fibrous materials, where the vinylidene chloride is copolymerized with carboxylic monomers and N-alkylol amide. U.S. Pat. No. 4,058,649 teaches a coating composition for coating thermoplastic film substrates, such a biaxially oriented polypropylene film substrate, which is heat sealable and which is an interpolymer of methacrylic acid and mixtures with acrylic acid, an alkyl acrylate, and vinylidene chloride.
Overpolymer compositions comprised of vinylidene chloride copolymers polymerized as layers over a core material are known for use as paper wraps, coated food films or containers. Examples of vinylidene chloride overpolymers are U.S. Pat. Nos. 3,291,768; 3,309,330; 3,379,665; 4,307,006; 4,898,782; 4,965,130; and 4,997,859. Most of these use a vinylidene chloride core or seed for the overpolymerization. In the case of U.S. Pat. Nos. 4,898,782; 4,965,130; and 4,997,859, the core layer is a copolymer of a methacrylate and an acrylate ester, because it imparts to the coated films the properties of high heat-seal strength, and the core seed particles are made by the extrusion polymerization of the two monomers.
Intertwined polymer networks in which a first polymer network is intertwined on a molecular scale with a second polymer network are known, such as is disclosed in U.S. Pat. No. 5,169,884 to M. K. Lindemann et al. The disclosed polymer is useful as a binder of fibers or fabric, such as fiberfill or as industrial or architectural coatings. The first polymer is an ethylenically unsaturated compound while the second polymer preferably contains styrene, but the phases are selected by their inability to polymerize conventionally. The intertwined polymer is formed by mixing the second monomer as an emulsion with the first polymer, which is also an emulsion, allowing them to equilibrate and then polymerizing.